Although bone is a mineralised tissue, it is cellular and metabolically active. The cells in bone are present on endosteal surfaces of cancellous bone adjacent to the marrow cavity, and within channels that tunnel through cortical bone known as the haversian systems. These cells are continually restructuring the skeleton. The bone restructuring or remodelling occurs in discrete packets known as bone-remodelling units.
The cells involved in the remodelling of bone are osteoclasts and osteoblasts. Osteoclasts are large multinucleated cells that are responsible for breaking down bone, and osteoblasts are small cuboidal cells that are responsible for synthesising new bone and then mineralising it. Osteoclasts are unique cells that are the only cells in the body known to have the capability of resorbing bone.
